SW5200602_Responce to Comments_20201020

Stantec Consulting Services Inc.
2127 Arysley Town Blvd. Suite 300, Charlotte, NC 28273
October 1, 2020
File: 178440214
Attention: Mr. Jim Farkas
North Carolina Department of Environmental Quality
Division of Energy, Mineral, & Land Resources Stormwater Program
512 N. Salisbury Street
1612 Mail Service Center
Raleigh, NC 27699
DearMr. Farkas,
Reference:Comment Response Letter
This is our response to comments received from your office onSeptember 29, 2020. We have reviewed
and addressed these comments and respond in the following manner:
1.Original Comment 4 Please provide sizing calculations showing that the level spreader-filter strip is
sized for the 10-year storm.
Calculation has been update to show that 10-year storm used to size the level spreader..
Please see Exhibit 8C.
2.Original Comment 5 Please do not provide rolls of plan sheets, but rather plans that are folded. Due
to space/budgetary constraints, we cannot store (either short-term for review or long-term as part of
the permit on-file) or mail rolls of plans. It is noted that some plans (C-000, C-200-202, C-300-307, &
C-603) were provided folded, but this is not the requisite 2x copies of all of the relevant sheets (It is
further noted that 2x copies of the plans were provided as large rolls, but for the reasons previously
mentioned, we require folded plans). I apologize if I was unclear in my original comment.
Only the folded sheets will be provided with copiesrevised report.
3.Original Comment 11a Please provide a hard copy of the cover page of the Supplement-EZ Form
with an original, ink signature.
A hard copy with original ink signature hasbeen provided.
4.Original Comment 11bPlease provide a SHWT boring in the area of proposed sand filter 1. Soil
boring 4 is close enough to sand filter 2 that it can be used to assess the SHWT elevation for that
SCM, but there are no provided borings close enough to sand filter 1 to accurately determine the
SHWT elevation for that SCM (Typically, we like to see the borings within the footprint of the SCM,
please refer to Part A-2 of the Manual for more information). Please also indicate either the ground
surface elevation or the boring termination elevation (bottom) for each boring so that the SHWT
elevation can be determined.

October 1, 2020
Mr. Jim Farkas
Page 2 of 3
Reference: Comment Response Letter
Additional boring at sandfilter 1 has been performed and its log has been added to Exhibit 3
and Exhibit 13. Existing surface elevations have been added on Exhibit 3 for reference.
Note: Boring log B-13 was added to the end of Exhibit 13 documentation.

5. Original Comment 12 While it is not required, it is recommended that the off-site drainage from
upstream properties be diverted around sand filter 2 since the Applicant cannot maintain control over
the development of property that they do not own. If the Applicant elects to account for off-site
drainage, it must either be accounted for at its full build-out potential (per 15A NCAC 02H .1003(3)(b))
or there must be a recorded legal agreement in place between the Applicant and the Owner of the
upstream property in which the Owner of the upstream property agrees to record a deed restriction
limiting the minimum/maximum amount of BUA on the upstream property that will be treated in the
ongoing maintenance costs will be handled, maintenance responsibility, a list of legal recourses
available to each party should one party fail to hold up their end of the agreement, and any other
related legal issues.

The flow calculation has been adjusted assuming the off-site tributary area received full
build out conditions. We consider this conservative as the majority of the area is within a
zoning buffer for the adjacent property. There was no change in sand filter size due to the
revised calculation.

6. Original Comment 13 Please clarify where the stage-storage tables, separated by sediment chamber
and sand chamber parts is located. The only stage-storage table that I could find is located within the
Hydraflow output. These stage-storage tables do not appear to be broken down by chamber type. IF I
missed these tables, please let me know where they can be found.

Stage-storage tables have been broken down by chamber type, see Exhibit 8B.

7. Original Comment 14ciii, Sand Filter Page, Line 18 If the SHWT is less than the boring termination
-
specific SHWT elevation is required for each sand filter.

There is no ground water encountered per the Geotech report and additional boring B-13
performed at the sandfilter 1 area. Existing surface elevations have been added on Exhibit 3
for reference. See boring logs added to Exhibit 3. The boring termination elevation has been
added to EZ form, line 18.

8. Supplement-EZ Form, Sand Filter Page, Line 10 This requirement is an MDC and must be met (if
comment.

This requirement for the MDC is to be met. Line 10 has been revised to Yes.

9. Supplement-EZ Form, Sand Filter Page, Line 22 The sand filters appear to be designed to attenuate
some peak flow amount (i.e. there is available storage in the facility in a
comment.

October 1, 2020
Mr. Jim Farkas
Page 3 of 3
Reference: Comment Response Letter
The sand filter chamber is design to pass the peak flow amount resulting in some
attenuation.Line 22 has been revised toYes.
10.Supplement-EZ Form, Sand Filter Page, Line 37 This item is the actual mechanism that disperses
flow over the sand chamber. Typical mechanisms include riprap weirs (Which these SCMs appear to
utilize), pipe networks, and/or level spreaders.
Ariprap weir is provided to disperse stormwater at the sand filter.Line 37 has been revised
to Weirs.
Regards,
Stantec Consulting Services Inc.
Jeff Rice, P.E.
Senior Principal
Phone:[phone]
[e-mail]
Attachment:
c.
fa document17